Axial compressor with tandem blades

ABSTRACT

Axial compressor with tandem blades consists of a compressor stage ( 1 ) with a double ( 2 ), or triple ( 3 ) blade arrangement, around an axial (A) rotor disk and corresponding stator (B), to increase the fluid flow deflection angle, with greater camber of the double, or triple profile, greater variation in isentropic total temperature and, consequently, greater rate of compression per stage, which can form multiple stages of the rotor and stator assembly with the same configuration of double or triple blades, providing the assembly with a greater rate of compression.

This is a request for a patent for the invention of an axial compressorwith tandem blades, especially an axial compressor comprised, by stage,of a rotor followed by a stator, repeated in series, including a frontblade, followed by at least one, or two, posterior blades arrangedaxially and circumferentially to each other. The posterior blade ispositioned to receive the flow from the frontal blade, or the centralone in the case of three blades, providing greater deflection of fluidflow, with greater camber of the double, or triple, profile of the rotorand respective stator, maintaining an acceptable overall efficiency andstability margin. Due to the high camber conditions in the rotor, thestator model follows the same order of double, or triple blades in orderto avoid fluid flow boundary layer separation on the blade suctionsurface and reposition it to the next rotor, in similar conditions tothat of the previous rotor. The last stator, at the compressor outlet,has the same number of blades as the rest, in order to release the flowwithout swirl in the axial direction. Blade profile is a result of thetype of flow and the compressor design.

The invented axial compressor has an application field in the gasturbine industry, turbo motors, propellants and a compressor assemblyfor generating gas or compressed air.

Technician in the matter knows that traditionally, conventional axialcompressors have a single blade assembly for each rotatory disk and itscorresponding stator.

Specifically, as per FIG. 7, the main parameters of the rotor andcorresponding stator, of the traditional axial compressor are:

-   -   Rotor tangential speed (rotation) U=ωr    -   Input axial speed in the rotor (u₁);    -   Input flow angle in the rotor (β₁);    -   Output flow angle (β₂) through rotor blades;    -   Absolute input speed of the rotor (V₁);    -   Absolute output speed of the rotor (V₂);    -   Relative input speed of the rotor (V_(1R));    -   Relative output speed of the rotor (V_(2R));    -   Input flow angle off the rotor (α₁);    -   Output flow angle off the rotor (α₂).

Angles (β₁ and β₂) in the conventional rotors are limited by virtue ofthe criteria adopted in flow calculations through the profile of theirblades. One of them, called the Haller criterion, the relative outputspeed (V_(2R)) cannot exceed the relative input speed (V_(1R)) in rotorblades of a value of around 0.72, because otherwise the losses would behigh. On the other hand, there is the criterion of losses based on thediffusion factor, referred to as the D-Factor, which also limits suchspeeds. Thus blade profile camber obeys a limit, which impedes greaterload on them, because if this criterion is exceeded, the flow losescontact with the blade profile, making the rotor lose its efficiency.

In the current state of the technique, some gas turbine axial compressorstator models have a dual blade configuration; however, in the laststage of compression. In this case, the stator assembly is a staticpiece and it does not exert work as in the rotor disks.

The dual blade configuration is also seen in some compression rotors,generating greater efficiency, called the booster effect, in the firststage, without a dual blade stator assembly.

In the document, U.S. Pat. No. 4,529,358, the configuration of the dualblades is slightly similar to this patent request; however the conceptis diverse. In this example, although the blades position themselves ina similar manner, the posterior blade has part of the leading edge inthe interior of the canal formed by the front blades, that is, theposterior blade overlaid the frontal blade, and the concept of operationis based on shock waves.

Another, subsonic model, however, with a dual profile position only inthe rotor and overlaid, that is, the second blade begins inside thefirst, but with a stator assembly of just one profile. In this case, thecompressor has its principle applied in flow efficiency only along therotor disk blades, not considering the gain in fluid deflection angle,as in the request claimed here.

Aware of the state of the technique and of the existing gap nozzle in itwas why the inventor, a person active in the segment in question, afterstudies and research, created the axial compressor with tandem blades,which is the object of this patent request, in which the rotor disk,with a double or triple blade arrangement, permits a greater variationin speeds related to output (V_(2R)) and input (V_(1R)), implying agreater camber between the input (β₁) and output (β₂) angles of fluidflow through the rotor channels, that is, a greater deflection of thefluid, resulting in greater efficiency regarding the increase inisentropic total temperature, and consequently, a greater rate ofcompression. Due to this effect in the rotor disk, the correspondingstator is obliged to have the same configuration of double or tripleblades along the crown in order to accommodate the flow at output in asituation that meets the similar conditions of subsequent rotor diskinput, or even the compressor output condition in the case of the laststage. Multiple stages of the rotor and stator assembly with the samedouble or triple blade configuration can be in juxtaposition to providea greater rate of compression for the whole assembly, thus formingstages of compression.

Below, the invention is explained with reference to the constructive andfunctional technical details, where, for a better understanding,reference is made to the attached drawings in which they are representedin an illustrative and unlimited manner:

FIG. 1: Lateral and upper cut perspective of the first stage of theaxial compressor with tandem blades;

FIG. 2: Detail of the double blade profiles in the rotor andcorresponding stator of the axial compressor with tandem blades;

FIG. 3: Detail of the triple blade profiles in the rotor andcorresponding stator of the axial compressor with tandem blades;

FIG. 4: Comparative triangle of rotor speeds of the axial compressorwith tandem blades with the rotor of the conventional axial compressor;

FIG. 5: Detail of the smaller blade profiles in the last channel formedby the second blade of the axial compressor with tandem blades;

FIG. 6: Schematic diagram of profiles of an axial compressor with tandemblades with two stages of compression;

FIG. 7: Schematic diagram showing the main parameters of the rotorassembly and corresponding stator of the axial compressor with tandemblades;

FIG. 8: Lateral and upper cut perspective of the first stage of theconventional axial compressor;

The axial compressor with tandem blades consists of a compressor (1)with a double (2), or triple (3) blade arrangement, around an axial (A)rotor disk and corresponding stator (B), to increase the fluid flowdeflection angle, with greater camber of the double, or triple profile,greater variation in isentropic temperature and, consequently, greaterrate of compression per stage, which can form multiple stages of therotor and stator assembly with the same configuration of double ortriple blades, providing the assembly with a greater rate ofcompression.

More specifically, the compressor (1) claimed is comprised, by stage, ofa set of double blades (2) as per the illustration in FIG. 2, or tripleblades (3) as illustrated in FIG. 3, tandem in a cluster configuration,one behind the other, involving the rotor disk (A) and its correspondingstator (B), providing greater camber of the double or triple profile,and greater deflection of the fluid flow (Δβ) without separation offluid flow contact with the suction surface of the profiles, which, ifit occurred could generate enormous losses. As illustrated in FIG. 4,observe that in the axial compressor with tandem blades, the radialspeed variation component (Δυ_(WTB)) is greater due to the increase inflow deflection through the profile, providing a higher Δβ value, which,in turn, permits a greater rate of compression. The principle claimed isbased on the smaller output angle β₂, which produces a greater fluidflow deflection angle, because Δ_(β1,2)=β₁−β₂, thus increasing totaltemperature variation, according to the expression:

${\Delta \; T_{t}} = \frac{\lambda \; {{Uu}_{1}\left( {{\tan \; {\beta 1}} - {{u_{2}/u_{1}}\tan \; {\beta 2}}} \right)}}{c_{p}}$

where:ΔT_(t)=total temperature variation in the stage;λ=correction factor;U=ωr=tangential do rotor speed;u₁ and u₂=axial components of the respective rotor input and outputspeeds;c_(p)=specific fluid heat.

Observe in the expression that the lower the value for tan β₂, that thistandem configuration of the compressor tends to approach zero, thegreater the ΔT_(t), consequently generating a greater rate ofcompression. The β₂ value is established and limited by the flowdiffusion criterion and, rigorously, also obeying the Haller numbercriterion, in which the ratio of relative output speeds through eachblade's channel (V_(2R)), and the input speed in the same blade'schannel (V_(1R)) is a ratio greater than or equal to 0.72. Thus, withthe compressor (1) with the tandem blade configuration, one has greaterdeflection in fluid flow, with a smaller Haller number through the rotorwith the controlled diffusion factor, D-Factor. As a result of greatdeflection in the rotor (A), its corresponding stator (B) should havethe same double (2) or triple (3) blade configuration in order to repeatthe same input conditions in the subsequent rotor. Regardless of havingdouble (2) or triple (3) blades, the posterior blade, in the rotor (A)as well as in the stator (B), is positioned where there is a gap nozzlebetween it and the blade in front, using the X and Y datum points shownin FIG. 2 as reference. The gap nozzle in the position of the posteriorblade in the axial direction occurs with X=0, that is, when the frontblade ends, the back blade begins in the same rotor disk, or in thestator cascade, but with gap Y in circumferential positioning, orbetter, the posterior blade is separated from the front blade at datumpoint Y, which is a function of compressor characteristics and it iscalculated to adjust flow through the channel. The Y gap datum point iscalculated to avoid minimizing the wake from the first blade, in orderto intervene as little as possible in second blade performance. Theprecise positioning of Y depends fundamentally on flow characteristics,in the sense of minimizing losses. For greater efficiency of thecompressor rotor, as illustrated in FIG. 5, an assembly of small blades,called splitter blades (4), one at each rotor output channel, can beused to improve fluid flow at rotor output. With the cluster arrangementof the rotor disk and stator, as illustrated in FIG. 6, one can formcompressors with multiples stages, greatly increasing the rate ofcompression.

What is claimed is:
 1. Axial compressor with tandem blades, wherein iscomprised, by stage, of an assembly of double (2) or triple (3) tandemblades in a cluster configuration involving the rotor disk (A) and itscorresponding stator (B), arranged one after the other in the axial andcircumferential direction, providing greater camber of the double ortriple profile, with greater deflection of fluid flow (Δβ) without fluidflow losing contact with the blade suction surface, greater variation inisentropic total temperature and greater rate of compression.
 2. Axialcompressor with tandem blades, according to claim 1, wherein theposterior blade, in the rotor (A) and stator (B), is positioned with agap nozzle in relation to the front blade; the gap nozzle in theposterior blade position in the axial direction occurs with X=0, whenthe front blade ends, the back blade begins in the same rotor disk, orin the stator cascade, but with a Y gap in the circumferentialpositioning.
 3. Axial compressor with tandem blades, according to claim2, wherein by the Y datum point as a function of flow through thechannel, calculated to avoid minimizing the wake from the first blade,in order to intervene as little as possible in second blade performance.4. Axial compressor with tandem blades, according to claim 1, whereinthe greater efficiency of the compressor rotor is due to his position inan assembly of small blades, cascade of splitter blades, (4) in therotor output channels.
 5. Axial compressor with tandem blades, accordingto claim 1, wherein there is a cluster arrangement of the rotor disk (A)and of the stator (B) in order to form compressors with multiple stages.